More accessibility fixes, smarter FAQ, layout tweaks.

Accessibility testing done using the online WAVE tool:

http://wave.webaim.org/report#/http%3A%2F%2Fstaging.datadryad.org%2F/ 

We're in good shape with these changes, but there's some minor cleanup (in DSpace/Java) for the Membership Application page:

http://wave.webaim.org/report#/http%3A%2F%2Fstaging.datadryad.org%2Fmembership/